The plugs are made of resilient silicone and they are perforated. This limits the amount of water entering your ear, but still permits equalization. Below 20 ft. some water will enter the space behind the earplug, but it is greatly limited by them.
I think I'll just keep shaking. Water only enters my ears at the water line - when the ear opening is half submerged so air can be exchanged for water. Something which lets water in at depth where I've never had water enter my ear in sounds worse to me - and probably would sound even worse once I emerged and started moving my head around